Energy, water, and electrolyte balance are among the most closely regulated parameters found in complexe organisms. Even a minor, uncorrected defect in the control of any one system could be life threatening. Most of the processes involved in these systems regulate internal use and conservation. Only one process, ingestion of food or fluids, can replenish exhausted supplies. The ultimate goal of the research outlined in this proposal is to understand the neural nechanisms that govern the decision to ingest or reject the contents of the oral cavity. Taste exemplifies the sensory events germaine to ingestion and rejection, but simplifies the system because a few, standard chemicals dissolved in water reliably elicit normal ingestion or rejection behavior. As with more complex food, the behavioral responses to gustatory stimuli respond to both immediate and remembered post-ingestional feedback. Using neuroanatomical electrophysiological and behavioral analysis, this project will follow gustatory afferent information as it ascends the neuraxis in order to ascertain at what neural levels different aspects of the ingestion or rejection decision are determined. Three related series of experiments contribute to this analysis: (1) After electrophysiologically located lesions in central gustatory structure, rats will be tested for their ability to use taste information in four behavioral and one endocrine response paradigms, (2) In neuroanatomical and acute neurophysiological experiments, neurons in the medulla and pons will be tested for their responses to both gustatory and visceral afferent stimuli and for their influence on the motoneurons that produce the oral aspects of ingestion anf rejection behavior, (3) Finally, chronic recording of single neuron discharges from behaving animals will be used to assess the way the nervous system responds to taste information during differing need states. In addition to contributing toward a basic understanding of how the nervous system coordinates diverse sensory information into precise physiological and behavioral control, this research has direct relevance to sensory mechanisms involved in the etiology of a variety of morbid conditions. Specifically, excess ingestion of carbohydrates (sugars and salt (sodium) is highly correlated with, and may be causally related to, obesity, diabetes, and hypertension.